For our Halloween preschool lesson the kids went to three different stations (science, math, and English). For our math station I taught the kids about counting to 20 and making bar graphs. I had 4 cauldrons full of different amounts of candy corns. As a group we counted the candy corns in each cauldron. Then, we graphed the amount and talked a little bit about which cauldron had more, which had less, etc.
Here's a picture of how they turned out. The bottom row of the graph is labeled "Cauldron #1, Cauldron #2, etc." I don't know how well they grasped the concept of graphing, but they liked counting the candy corns and then playing witch pitch later. (To read about witch pitch click on the link.)